Disclosed herein are ink carriers, phase change inks and methods for making same. More specifically, disclosed herein are ink carriers including (A) an antioxidant mixture comprising (a) a hindered phenol antioxidant, and (b) a hindered amine antioxidant, (B) a polyalkylene wax, (C) a functional wax, and (D) an ester-terminated amide, and phase change inks including such ink carriers which can be used in direct and indirect printing processes. One embodiment of this disclosure is directed to a phase change ink composition comprising (1) a colorant and (2) an ink carrier which comprises (A) an antioxidant mixture comprising (a) a hindered phenol antioxidant, and (b) a hindered amine antioxidant, (B) a polyalkylene wax, (C) a functional wax, and (D) an ester-terminated amide, the low polarity ink carrier being substantially resistant to phase separation, having excellent thermal stability, resisting autocatalytic degradation of the ink composition and a substantial color shift upon standing, and providing enhanced humidity resistance, said low polarity ink having a substantially low surface energy. Another embodiment is directed to a method which comprises (a) incorporating into an ink jet printing apparatus a phase change ink composition comprising (1) the low polarity ink carrier described above, and (2) a colorant; (b) melting the ink; (c) causing droplets of the melted ink to be ejected in an imagewise pattern; and (d) transferring the ink in the imagewise pattern to a final recording substrate.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the printhead operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. Nos. 4,889,560, 4,889,761, and 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labeling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with inks that are liquid at room temperature are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known and are described in U.S. patent application Ser. No. 10/881,047, now U.S. Pat. No. 6,989,052 the disclosure of which is totally incorporated herein by reference.
U.S. Pat. Nos. 5,783,657, 5,998,570 and WO 98/17704, (Pavlin et al), the disclosures of which are totally incorporated herein by reference, disclose a low molecular weight, ester-terminated polyamide that may be blended with a liquid hydrocarbon to form a transparent composition having gel consistency. The ester-terminated polyamide is prepared by reacting “x” equivalents of dicarboxylic acid wherein at least 50 percent of those equivalents are from polymerized fatty acid, “y” equivalents of diamine such as ethylene diamine, and “z” equivalents of monoalcohol having at least 4 carbon atoms. The stoichiometry of the reaction mixture is such that 0.9≦{x/(y+z)}≦1.1 and 0.1≦{z/(y+z)}≦0.7. The reactants are heated until they reach reaction equilibrium.
U.S. Pat. No. 6,111,055 (Berger, et al), the disclosure of which is totally incorporated herein by reference, discloses an ester terminated dimer acid-based polyamide which is blended with a solvent to form a gel. The solvent may be flammable, and a wick may be added to the resulting gel to form a candle. The said ester terminated dimeracid-based polyamide is prepared by thermal condensation of a diacid, a diamine and a monoalcohol.
A need remains for improved phase change inks, and more specifically, low energy solid inks which permit phase change ink jet printers to perform at more moderate operating conditions than with conventional phase change inks. For example, a need exists for phase change inks which can be jetted at temperature lower than conventional jetting temperature as described below. Also, there is a need for phase change inks having enhanced humidity resistance. In addition, a need remains for phase change inks having low surface energy and improved thermal stability. A need also remains for certain ink carrier components and compositions which reduce the rate of oxidation at high temperature, thereby minimizing degradation of the ink components, and can delay the onset of oxidation itself. Further, a need remains for phase change inks that maximize long term stability and provide improved compatibility of the ink components. Additionally, a need remains for phase change inks that print successfully on paper and transparency stock. In addition, there is a need for phase change inks that generate prints with good performance in automatic document feeders as a result of their low surface energy.